One of the most important issues in modern condensed matter physics is the realization of fractionalized excitations, such as the Majorana excitations in the Kitaev quantum spin liquid. The 3d-based Kitaev candidate Na2Co2TeO6 is promising to realize such kind of spin liquid phase under external magnetic fields. Here, we first established a complete phase diagram comprising an intermediate magnetically disordered phase sandwiched by the zigzag ordered phase and the polarized trivial phase by the in-plane magnetic torque measurements. Then, the observations, including the restoration of the crystalline point group symmetry in the angle-dependent torque data and the coexisting spinons and magnons from the inelastic neutron scattering data, provide strong evidence that this disordered phase is a field induced quantum spin liquid with partially polarized spins. Our variational Monte Carlo simulation with the effective K-J1-Γ-Γ′-J3 model agrees well with the experimental data and further supports this conclusion.
We report the nontrivial topological states in an intrinsic type-II superconductor BaSn
5
(T
c ∼ 4.4 K) probed by measuring the magnetization, specific heat, de Haas–van Alphen (dHvA) effect, and by performing first-principles calculations. The first-principles calculations reveal a topological nodal ring structure centered at the H point in the k
z = π plane of the Brillouin zone, which could be gapped by spin-orbit coupling (SOC), yielding relatively small gaps below and above the Fermi level of about 0.04 eV and 0.14 eV, respectively. The SOC also results in a pair of Dirac points along the Γ–A direction, located at ∼ 0.2 eV above the Fermi level. The analysis of the dHvA quantum oscillations supports the calculations by revealing a nontrivial Berry phase originating from the hole and electron pockets related to the bands forming the Dirac cones. Thus, our study provides an excellent avenue for investigating the interplay between superconductivity and nontrivial topological states.
We report results of magnetization, specific heat, and muon spin relaxation (μSR) measurements on single crystals of disorder-free Yb 3+ triangular lattice Yb(BaBO 3 ) 3 . The magnetization experiments show anisotropic magnetic properties with Curie-Weiss temperatures θ ⊥ = −1.40 K (H ⊥ c) and θ = −1.16 K (H c) determined from low-temperature data. The absence of both long-range antiferromagnetic order and spin freezing is confirmed down to 0.27 K at zero field. A two-level Schottky anomaly due to the opening of the ground-state Kramers doublet is observed from the low-temperature specific heat measurements when the applied magnetic fields μ 0 H > 0.7 T. At zero field, the increase of both C mag /T and the muon spin relaxation rate λ below 1 K is due to the electronic spin excitations, which often exist in quantum magnets where dipole-dipole interactions create an anisotropy of magnetic properties. The spin excitation is also supported by the unusual maximum of the field dependence of λ due to the field-induced increase in the density of excitations. We argue that dipolar interaction is dominant and induces the spin dynamics in the quantum magnet Yb(BaBO 3 ) 3 .
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